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diff --git a/numpy/fft/info.py b/numpy/fft/info.py deleted file mode 100644 index cb6526b44..000000000 --- a/numpy/fft/info.py +++ /dev/null @@ -1,187 +0,0 @@ -""" -Discrete Fourier Transform (:mod:`numpy.fft`) -============================================= - -.. currentmodule:: numpy.fft - -Standard FFTs -------------- - -.. autosummary:: - :toctree: generated/ - - fft Discrete Fourier transform. - ifft Inverse discrete Fourier transform. - fft2 Discrete Fourier transform in two dimensions. - ifft2 Inverse discrete Fourier transform in two dimensions. - fftn Discrete Fourier transform in N-dimensions. - ifftn Inverse discrete Fourier transform in N dimensions. - -Real FFTs ---------- - -.. autosummary:: - :toctree: generated/ - - rfft Real discrete Fourier transform. - irfft Inverse real discrete Fourier transform. - rfft2 Real discrete Fourier transform in two dimensions. - irfft2 Inverse real discrete Fourier transform in two dimensions. - rfftn Real discrete Fourier transform in N dimensions. - irfftn Inverse real discrete Fourier transform in N dimensions. - -Hermitian FFTs --------------- - -.. autosummary:: - :toctree: generated/ - - hfft Hermitian discrete Fourier transform. - ihfft Inverse Hermitian discrete Fourier transform. - -Helper routines ---------------- - -.. autosummary:: - :toctree: generated/ - - fftfreq Discrete Fourier Transform sample frequencies. - rfftfreq DFT sample frequencies (for usage with rfft, irfft). - fftshift Shift zero-frequency component to center of spectrum. - ifftshift Inverse of fftshift. - - -Background information ----------------------- - -Fourier analysis is fundamentally a method for expressing a function as a -sum of periodic components, and for recovering the function from those -components. When both the function and its Fourier transform are -replaced with discretized counterparts, it is called the discrete Fourier -transform (DFT). The DFT has become a mainstay of numerical computing in -part because of a very fast algorithm for computing it, called the Fast -Fourier Transform (FFT), which was known to Gauss (1805) and was brought -to light in its current form by Cooley and Tukey [CT]_. Press et al. [NR]_ -provide an accessible introduction to Fourier analysis and its -applications. - -Because the discrete Fourier transform separates its input into -components that contribute at discrete frequencies, it has a great number -of applications in digital signal processing, e.g., for filtering, and in -this context the discretized input to the transform is customarily -referred to as a *signal*, which exists in the *time domain*. The output -is called a *spectrum* or *transform* and exists in the *frequency -domain*. - -Implementation details ----------------------- - -There are many ways to define the DFT, varying in the sign of the -exponent, normalization, etc. In this implementation, the DFT is defined -as - -.. math:: - A_k = \\sum_{m=0}^{n-1} a_m \\exp\\left\\{-2\\pi i{mk \\over n}\\right\\} - \\qquad k = 0,\\ldots,n-1. - -The DFT is in general defined for complex inputs and outputs, and a -single-frequency component at linear frequency :math:`f` is -represented by a complex exponential -:math:`a_m = \\exp\\{2\\pi i\\,f m\\Delta t\\}`, where :math:`\\Delta t` -is the sampling interval. - -The values in the result follow so-called "standard" order: If ``A = -fft(a, n)``, then ``A[0]`` contains the zero-frequency term (the sum of -the signal), which is always purely real for real inputs. Then ``A[1:n/2]`` -contains the positive-frequency terms, and ``A[n/2+1:]`` contains the -negative-frequency terms, in order of decreasingly negative frequency. -For an even number of input points, ``A[n/2]`` represents both positive and -negative Nyquist frequency, and is also purely real for real input. For -an odd number of input points, ``A[(n-1)/2]`` contains the largest positive -frequency, while ``A[(n+1)/2]`` contains the largest negative frequency. -The routine ``np.fft.fftfreq(n)`` returns an array giving the frequencies -of corresponding elements in the output. The routine -``np.fft.fftshift(A)`` shifts transforms and their frequencies to put the -zero-frequency components in the middle, and ``np.fft.ifftshift(A)`` undoes -that shift. - -When the input `a` is a time-domain signal and ``A = fft(a)``, ``np.abs(A)`` -is its amplitude spectrum and ``np.abs(A)**2`` is its power spectrum. -The phase spectrum is obtained by ``np.angle(A)``. - -The inverse DFT is defined as - -.. math:: - a_m = \\frac{1}{n}\\sum_{k=0}^{n-1}A_k\\exp\\left\\{2\\pi i{mk\\over n}\\right\\} - \\qquad m = 0,\\ldots,n-1. - -It differs from the forward transform by the sign of the exponential -argument and the default normalization by :math:`1/n`. - -Normalization -------------- -The default normalization has the direct transforms unscaled and the inverse -transforms are scaled by :math:`1/n`. It is possible to obtain unitary -transforms by setting the keyword argument ``norm`` to ``"ortho"`` (default is -`None`) so that both direct and inverse transforms will be scaled by -:math:`1/\\sqrt{n}`. - -Real and Hermitian transforms ------------------------------ - -When the input is purely real, its transform is Hermitian, i.e., the -component at frequency :math:`f_k` is the complex conjugate of the -component at frequency :math:`-f_k`, which means that for real -inputs there is no information in the negative frequency components that -is not already available from the positive frequency components. -The family of `rfft` functions is -designed to operate on real inputs, and exploits this symmetry by -computing only the positive frequency components, up to and including the -Nyquist frequency. Thus, ``n`` input points produce ``n/2+1`` complex -output points. The inverses of this family assumes the same symmetry of -its input, and for an output of ``n`` points uses ``n/2+1`` input points. - -Correspondingly, when the spectrum is purely real, the signal is -Hermitian. The `hfft` family of functions exploits this symmetry by -using ``n/2+1`` complex points in the input (time) domain for ``n`` real -points in the frequency domain. - -In higher dimensions, FFTs are used, e.g., for image analysis and -filtering. The computational efficiency of the FFT means that it can -also be a faster way to compute large convolutions, using the property -that a convolution in the time domain is equivalent to a point-by-point -multiplication in the frequency domain. - -Higher dimensions ------------------ - -In two dimensions, the DFT is defined as - -.. math:: - A_{kl} = \\sum_{m=0}^{M-1} \\sum_{n=0}^{N-1} - a_{mn}\\exp\\left\\{-2\\pi i \\left({mk\\over M}+{nl\\over N}\\right)\\right\\} - \\qquad k = 0, \\ldots, M-1;\\quad l = 0, \\ldots, N-1, - -which extends in the obvious way to higher dimensions, and the inverses -in higher dimensions also extend in the same way. - -References ----------- - -.. [CT] Cooley, James W., and John W. Tukey, 1965, "An algorithm for the - machine calculation of complex Fourier series," *Math. Comput.* - 19: 297-301. - -.. [NR] Press, W., Teukolsky, S., Vetterline, W.T., and Flannery, B.P., - 2007, *Numerical Recipes: The Art of Scientific Computing*, ch. - 12-13. Cambridge Univ. Press, Cambridge, UK. - -Examples --------- - -For examples, see the various functions. - -""" -from __future__ import division, absolute_import, print_function - -depends = ['core'] |